Self-attaching female fastener elements including pierce and clinch nuts were developed by Multifastener Corporation, the predecessor in interest of the Assignee of this application. Pierce and clinch nuts are generally installed in a metal panel in a die press which may also be utilized to form the panel, wherein an installation head is installed in one die shoe or platen of the die press, generally the upper die shoe, and a die member or die button is installed in the other die shoe, generally the lower die shoe. The installation head receives the self-attaching fasteners and the fasteners are then installed by a reciprocating plunger in the installation head with each stroke of the die press. U.S. Pat. Nos. 3,187,769, 3,648,747 and 3,711,931, all assigned to the Assignee of the predecessor in interest of the Assignee of the present application, illustrate the types of self-attaching female fasteners available from the Assignee of this application.
Self-attaching female fasteners may alternatively be utilized as pierce or clinch nuts, wherein pierce nuts pierce an opening in the panel and clinch nuts are installed in a pre-pierced panel opening. The self-attaching fasteners illustrated in the above-referenced patents are formed by rolling, wherein a metal wire is progressively rolled into a nut strip having the cross-section of the desired fastener, the strip is then pierced, forming the nut bore, and the rolled section is then chopped or severed to provide the desired length. The nut bore is then generally tapped and the self-attaching female fastener is ready for installation as described above. Such fasteners are presently used in mass production applications, such as used by the automotive and appliance industries. The pierce nuts disclosed in the above-referenced U.S. Pat. Nos. 3,648,747 and 3,711,931 have superior performance characteristics including improved push-off strength and provide a flush mounting on the panel. The improved push-off strength is provided by the parallel “re-entrant” grooves in the flange portions adjacent the pilot portion. As used herein, a “re-entrant” groove includes a bottom wall and relatively inclined side walls, wherein the entrance to the groove at the flange portion has a width which is smaller than the width of the bottom wall of the groove providing a more secure retention of the panel deformed into the groove. The panel is deformed into the groove by a die member or die button having parallel lips which deform the panel against the bottom wall of the grooves and beneath the inclined side wall or walls of the grooves. In one preferred embodiment, both side walls of the grooves are relatively inclined forming parallel dovetail-shaped grooves providing superior performance. However, a re-entrant groove may have only one inclined side wall, preferably the outer groove side walls furthest from the pilot.
As will be understood by those skilled in this art, the self-attaching fasteners described above formed by rolling are limited in shape. That is, the rolled nut must be generally rectangular including a rectangular pilot portion having a rectangular end face and rectangular flange portions on opposed sides of the pilot portion, each having an end face generally spaced below the end face of the pilot portion and the parallel re-entrant grooves are formed in the flange portions adjacent the pilot portion. However, in certain applications, it would desirable for a pierce nut to have a round or generally cylindrical pilot portion and a flange portion which surrounds the pilot portion, which cannot be presently formed by conventional roll forming techniques.
The method of forming the self-attaching female fastener element of this invention is disclosed in a co-pending application filed concurrently herewith. The self-attaching female fastener element of this invention is particularly suitable for applications requiring a seal between the female fastener and the panel following installation, such as an oil or transmission pan nut as disclosed herein. The method of this invention forms a sealed joint between the female fastener and the panel assembly and may be installed in a panel by a conventional die press with one stroke of the die press as further disclosed below.